Kemp said, "Casey Cagle is collapsing in the polls, and this endorsement is a last minute attempt to distract voters from the secret recording where Cagle insults conservatives and confesses to trading votes for campaign cash."

But Deal said, in the end, he felt that Cagle could best carry on his legacy of reform and economic development.

"For that reason, I believe that Casey Cagle will be the best candidate for that position as governor of this state," Deal said.

"This is a man with great integrity and great character and to have his confidence reflects, obviously, exactly the type of governor which I am going to be," Cagle said.

Whoever emerges from the nine-week runoff will face a November showdown against former House Minority Leader Stacey Abrams, a competition that will test whether the state is competitive after more than a decade of Republican rule.